It is never explained who Ferb's mother is, or who Phineas and Candace's father is.
As of 2015, it is the longest running Disney animated show, lasting from 2007 to 2015.
It took Creators Dan Povenmire and Jeff 'Swampy' Marsh sixteen years to get this show on television.
Ferb (Thomas Brodie-Sangster) has a crush on Vanessa Doofenshmirtz (Olivia Olson). In Love Actually (2003), Sam (Thomas Brodie-Sangster) learns to play the drums, so that he can impress Joanna (Olivia Olson).
Director and Creator Dan Povenmire, and Director Zac Moncrief left Family Guy (1999) to work on this show.
The first drawing of Phineas was on a piece of butcher's paper, drawn with crayon in a restaurant.
Ferb rarely talks. In fact, there are many episodes in which he has no lines at all. (According to Phineas, "Ferb's more of a man of action".)
Sometimes Jeremy works at "Mr. Slushy Burger", and sometimes he works at "Mr. Slushy Dog".
According to Dan Povenmire, Phineas and Ferb's humor style is sort of a hybrid between Family Guy (1999) and SpongeBob SquarePants (1999), two shows that he had worked on.
It is hinted in the series that Dr. Doofenshmirtz could be German, the word "Doof" in his name is German for stupid or idiot.
Each episode contains at least one original song. The writing staff sings the song into the answering machine of Danny Jacob on Fridays to have it be magically written each Monday.
Jaret Reddick, lead singer of the band Bowling for Soup, which does the theme song for this show, is the voice of Danny, lead singer of the fictitious band Love Händle in the series.
Ferb's "large eye" changes depending on what direction he's facing. The large one is always the one furthest away from the screen.
The giant floating baby head, which was first featured in Phineas and Ferb: One Good Scare Ought To Do It!: Parts 1 & 2 (2008), became a running gag in the series. According to Dan Povenmire, the baby head came from "one board panel drawn by Michael Diederich, and one of our directors, Robert Hughes thought it was hilarious, and made a whole bit about it. Now it shows up all the time."
The show takes place in Danville, which is in Jefferson County, which is in the tri-state area. Danville is named after Dan Povenmire, and Jefferson County is named after Jeff 'Swampy' Marsh.
There are one hundred four days in summer vacation, yet the series has one hundred sixty episodes. However it is possible that the winter vacation episodes take place between summers.
While other characters simply call him Perry, Dr. Doofenshmirtz always refers to Perry by his full name (Perry the Platypus). He doesn't abbreviate the names of his other nemeses either (Peter the Panda, Planty the Potted Plant, et cetera).
Major Monogram said "Great Googly Moogly!", which was a quote from Maggie and the Ferocious Beast (1998), Evolution (2001), and a 1957 song by Sid Bradley.
Dr. Doofenshmirtz's robot-man "Norm" was originally a robot to target platypuses. In later episodes, he is seen as his servant.
Dr. Doofenshmirtz name was originally Dr. Meddleshmirtz. Both also have the same number of letters, thirteen.
Candace's best friend Stacy is sisters with Ginger, one of the girls in Isabella's Fireside Girl troop.
Several songs have been re-used, such as Phineas and Ferb's mom's one hit wonder song, that was later played as elevator music, and the Love Händel hit playing on the radio for Dr. Doofensmirtz.
It has been seen in several episodes that Ferb has a crush on Dr. Doofenshmirtz's daughter Vanessa.
Dan Povemire and Jeff "Swampy" Marsh created the show, and voiced Dr. Doofenshmirtz and Major Monogram, respectively.
There's a theory that Doofenshmirtz is the biological father of Candace and Phineas, because both Phineas and Doof has triangular heads, both Candace and Doof have long necks, and there is an episode in which Linda and Doof are seen on a date. If Doof is Candace and Phineas's biological father, then it would be assumed that Doof had an extramarital affair with Linda because Candace and Vanessa are the same age, and Vanessa remembers when her mother and father were married before they divorced.
Phineas and Ferb Get Busted, Phineas and Ferb's Quantum Boogaloo, Wizard of Odd and Ferb TV are the only 4 times there has just been a single plot line revolving around Phineas, Candace and Ferb. Additionally, Road to Danville, This is Your Backstory, Sidetracked and Live and Let Drive are the only 4 times there has just been a single plot line revolving around Perry and Dr. Doofenshmirtz.
Richard O'Brien (of Rocky Horror Picture Show) voices Lawrence Fletcher. In some episodes he, or one of the characters, makes a reference to The Rocky Horror Picture Show.
Phineas is right-handed, as shown when he plays the guitar in "Summer", and uses the baseball bat in Phineas and Ferb the Movie: Across the 2nd Dimension (2011).
Thomas Brodie-Sangster, the person who voiced Ferb, recorded his audio in the UK and sent it to the US. Because Ferb almost never spoke, it wasn't necessary that his voice actor lived near production.
Most of Doofenshmirtz's inventions actually do work, it's just that they're so ridiculous and absurd that they don't actually allow him to take over the Tri-State Area/World.
Dee Bradley Baker (Perry) plays Diogee on Milo Murphy's Law (2016). Additionally, Dan Povenmire and Jeff "Swampy" Marsh also play Dakota and Cavendish on Milo Murphy's Law, as well.